Tracking down clues to help solve crimes

Ti Gong

At a crime scene, even forensic evidence too small to see with the naked eye can be crucial in solving a whodunit. Enter Cai Nengbin, 50, a police officer and senior engineer who has spent nearly a quarter century tracking down those minute traces.

Cai is an inventor and tutor of new-generation forensic specialists, with 31 patents and numerous awards to attest to his skills.

“The first day of forensic studies at the police academy, a professor said to us, ‘You are first officers and then university students, and you are the future of forensic science in China’,” Cai recalls.

Crime scene photography records physical evidence for use in case prosecution and provides help in identifying suspects and sequence of events.

At a typical crime scene, a group of investigators first conducts a preliminary survey and secures the site against possible contamination. Then medical examiners arrive to examine dead bodies, if the case involves deaths. Investigators then flag evidence sites for crime scene photographers.

That’s where Cai’s work began. Despite all the years behind him, he still remembers the first murder scene he attended as an intern at age 22. A young woman was strangled in Pudong and left to die in bushes. “She was so young, about my age, and I saw imprints on her neck,” he says. “I wanted to find the murderer.”

To photograph something hardly visible to the naked eyes, one can shed what is called “invisible light” on an object and gather reflected light from it with a camera. The technology was available in 1995 when Cai started at the police research institute, but it was in its infancy. The research institute of Shanghai’s criminal investigation department owned a huge machine for the purpose, but it was impossible to transport it to scenes of crime, Cai says.

“It was hard to take clear pictures on first attempts, so we often used a basin or a bucket to cover the evidence and returned later to take more pictures until we got photos that were clear enough to be used as evidence,” he says.

In one murder case, Cai and his colleagues even set up a temporary dark room at a crime scene, he remembered. The somewhat bulky equipment available at the time prompted Cai and his team to look for more efficient methods of capturing evidence.

To be able to apply a very strong, pure light source of light was the goal, and by 2011, Cai and his team had patented new devices and methods.

“China is a leading country in the world in this field, and our inventions have aroused interest from some of the world’s top scientists,” Cai says.

His pioneering methods proved to work especially well in taking pictures of evidence on smooth surfaces, such as glass or paper, which otherwise were hard to photograph.

Ti Gong

Cai recalls one case in suburban Jinshan District where a woman was found dead by the sea.

Police found a medical exam record on the woman’s body, but on the piece of paper, only the name of the street was discernible to the naked eye. Since there was a street of the same name in downtown Shanghai, police went there to investigate, but there was no clinic at the address.

Using a device developed by Cai’s lab, forensic inspectors were able to bring into focus a faded stamp of the medical institute and found out that the address was in the southwestern city of Chongqing. The woman was later deemed to have committed suicide.

In a murder case in Hongkou District, the technology generated a clear picture of an imprint on adhesive tape, which led to the arrest of a suspect.

The technology enabled 20 percent more imprints to be taken from crime scenes, according to the police, but Cai didn’t stop there.

In recent years, new technologies developed in Cai’s lab have increased that rate beyond 20 percent.

Cai’s other inventions include a device patented in 2015 that can scan a cylindrical object and take pictures of evidence on its surface.

The device was born out of the necessity to lift prints left on entrances to buildings or rooms, such as doorknobs and window frames. The scanned object is placed on a disc whose turning speed is controlled by a computer.

Since too much exposure to invisible light can impair the health of photographers, Cai also invented and patented a light with a “lampshade” that is connected to the top of the camera. The lampshade is pressed to the surface where the imprint is located when the photographer snaps the shot so that the light leaked into the environment is reduced as little as possible.

From 2009 to 2015, Shanghai police solved at least 95 percent of all murder cases every year. In the past two years, 100 percent of all murders were solved, according to the police. This performance places them in a leading position among all cities in China.

Despite the statistics, Cai is still exploring new ways to take clearer pictures of forensic evidence.

“I hope the use of invisible light will one day be able to discern even more about imprints,” he says.

Cai, whose daughter is also a member of the police force, says photography is a hobby in his spare time.

“I enjoy it more when I’m off duty because then it becomes more an art form then a workplace technology,” he says.